1. Field of the Invention
The present invention relates to aircraft steerable main landing gear and more particularly to main landing gear for larger aircraft where wheels per landing gear and/or gears per aircraft increase.
2. Description of the Prior Art
In the patent literature, U.S. Pat. No. 2,567,074 to Kupiec; U.S. Pat. No. 2,682,311 to Bishop; and U.S. Pat. No. 3,516,625 to Hauser, et al. are illustrative of steering which is accomplished by pivoting the entire truck about a vertical axis as a single unit. Control of relative rotation between trucks is accomplished by a variety of means in these systems.
U.S. Pat. No. 2,630,285 to Geisse shows a means of coupling pairs of wheels on a common axis using kingpins and tierods. Systems are shown for both single and multiple axle landing gear trucks. In contrast to the present system, castered wheels are shown for self alignment. There is no mechanism for steering the wheels.
Great Britain Patent No. 904,783 is exemplary of load equalization techniques wherein there is shown wheel truck where wheel pairs articulate about a longitudinal axis so as to equalize wheel loads when an aircraft encounters transverse terrain contours.
U.S. Pat. No. 4,917,334 to Ralph et al. shows a multi-wheeled trailing type landing gear. In this configuration, the forward axle (2 wheels) is mounted directly to the shock strut. The aft two axles, 2 wheels each, are mounted on a truck which is cantilevered from the aft side of the strut on a pivoting radius arm. Shock absorbers are used to react the vertical loads. This is in contrast to the present load equalization where a primary truck is pivoted on the shock strut, and secondary trucks are pivoted on the ends of the primary strut.
As aircraft get progressively larger, wheels per landing gear (and/or gears per aircraft) increase the amount in order to offset the problems in flotation and tire loading limitations.
However, as the number of wheels and gears increase, so does the reluctance of the main landing gear to allow the aircraft to turn during steering.
The main landing gears increasing adhesion to the ground (tracking) causes a reducing adhesion to the ground at the nose gear. When the ground adhesion at the nose gear approaches zero, the directional control of the aircraft during taxi is greatly decreased.
During tractor towing operations, the nose gear steering angle is governed by the tractor but heavy torsional loads can be induced into the main landing gears resulting in heavy designs.
The above problems have resulted in the incorporation of the "body gear steering system". However, without the advantage of load equalization the turning moments due a one tire flat situation, are reacted by the steering actuators. This results in exceptionally large and heavy actuators.